The invention relates to a system and method for correcting corneal irregularities through reshaping of an eye""s cornea to provide a desired corrective corneal curvature. A preferred embodiment of the invention includes a topography device for mapping in detail the irregularities and surface deviations of a cornea, an interface system for receiving and manipulating topographical data and for providing directions to a laser system or the like to carry out a predetermined ablation profile on a substrate such as a corneal stroma and for providing a variety of actual and simulated pre and post operative visual depictions. The interface system provides a tool for use by a surgeon or the like which allows a surgeon to review and simulate a wide variety of potential surgical alternatives for a wide variety of corneal defects including irregular eye shapes and corneal surface irregularities.
For many, many years, humans have sought ways to correct visual problems. The ancient Chinese slept with small bags of mercury on their eyes, flattening their corneas and improving their shortsightedness. Unfortunately, the effects only worked for a few minutes after waking. Spectacles are thought to have been first introduced by the Arabs in the 11th Century and were introduced into Europe about 200 years later. This century has seen the development of contact lenses, initially the hard variety and later soft and disposable soft lenses.
Although these optical aids allow patients to see well while wearing them, they do not offer a permanent cure for the visual disorder or problem, and in some situations even glasses and contacts cannot provide complete correction due, for example, to a localized, highly irregular shaped corneal defect. Also, in many situations, they are inappropriate, for example, when swimming or wearing contacts in the laboratory. Another problem is that in some instances dangerous situations can arise when they become dislodged. This can occur while they are being used by firefighters and police officers.
Roughly two decades ago, surgical techniques were introduced in an effort to permanently correct shortsightedness and astigmatism. The radial keratotomy procedure used a diamond blade to make incisions into the cornea, the front surface or xe2x80x9cwindow of the eyexe2x80x9d. Although this technique worked relatively well, there have been problems with long term stability of vision and weakening of the cornea as a result of the cuts often having to be made up to 95% of the corneal thickness.
More recently, these older techniques have been replaced with laser treatment techniques which have replaced the surgeon""s blade with a computer controlled laser that gently re-sculptures the shape of the cornea without cutting or, for most applications, weakening the eye. These laser techniques are typically carried out with a photoablation process using an excimer laser.
Excimer lasers were chiefly developed for the manufacture of computer microchips, where they were used to etch the circuits. However, the laser""s extreme accuracy and low thermal effect resulted in it being well suited as an eye laser. That is, many eye lasers are extremely accurate and remove only 0.25 microns (1/4000th millimeter) of tissue per pulse. During the re-sculpturing, the excimer laser gently xe2x80x9cevaporatesxe2x80x9d or vaporizes tissue; there is no burning or cutting involved. In most cases, the laser treatment takes only 20 to 45 seconds, depending on how severe the refractive error is. A fast treatment time is important in that, for some procedures, an overextended treatment period can slow the post operative curing process to final vision level obtainment.
In the normal eye, light rays entering the eye are accurately focused on the retina and a clear image is formed. Most of the bending or focusing of the light rays occurs at the cornea, with the natural lens inside the eye being responsible for fine adjustments. If light is not focused on the retina, then the eye is said to have a refractive error. Common refractive errors include: myopia or shortsightedness, hyperopia or farsightedness, and astigmatism. The excimer laser has been used to re-sculpture the cornea in myopia, hyperopia and astigmatism corrections in an effort to make the curve of the cornea focus light rays normally on the retina.
Myopia, or shortsightedness, is a condition whereby light rays come to a focus in front of, rather than on, the retina at the back of the eye. This results in blurry vision, especially when looking at objects far away. Myopia results from the length of the eye being too long or the cornea being too steeply curved.
In hyperopia, or farsightedness, light rays are focused behind the retina. This results in blurry vision especially when looking at objects that are close. Hyperopia results from the length of the eye being too short or the cornea being too flat.
In astigmatism, the cornea, or window of the eye, has an irregular curvature being shaped more like a rugby ball, rather than a soccer ball. Light rays are focused at different points. A person often has some degree of astigmatism and myopia or hyperopia at the same time. Any surface contour irregularities can also result in the improper focusing of the eye due to the irregularities causing light rays to land away from the desired focal point on the retina.
In myopia laser correction procedures, the cornea is flattened to better focus light rays normally on the retina, whereas in hyperopia, the cornea is made more curved. With astigmatism, the surface of the cornea is re-sculptured to a regular curvature.
Presbyopia is a problem considered to be due to an aging process occurring in the natural lens of the eye, and thus does not fall under the same category as the refractive errors of myopia, astigmatism and hyperopia noted above, although combinations of presbyopia and one or more of the refractive errors are possible. U.S. Pat. No. 5,533,997 to Dr. Luis A. Ruiz describes a presbyopia corrective apparatus and method which involves the use of a laser system to remove tissue from the eye in presbyopic corrective patterns discovered to be effective by the inventor.
One of the prior art laser treatment methods is known as photorefractive keratectomy (PRK), in which the laser beam is applied directly to the surface of the cornea, after the thin surface layer of epithelium cells has been removed (e.g., through solvent with wiping, preliminary laser treatment, or minor abrasion). After the direct laser re-sculpturing of the cornea, a bare area of the cornea is left which takes a few days to heal (e.g., 2 to 6 days) and can be uncomfortable during this period. The healing process can sometimes lead to regression (some refractive error returns) or to scarring (which may blur the vision), especially in patients with large refractive errors. Although still used for low degrees of myopia and hyperopia, PRK is generally being replaced by the LASIK method for these same disorders, in which the laser treatment is applied under a protective comeal flap. Under the xe2x80x9cLaser in situ Keratomileusisxe2x80x9d (LASIK) treatment, a thin protective corneal flap is raised, rather like a trapdoor. The front surface of the exposed cornea is treated by the excimer laser. The net result being that the cornea is altered in a manner directed at allowing light rays to be focused normally on the retina. At the end of the procedure, the protective flap is simply replaced. The LASIK technique leaves the original surface of the cornea virtually intact, hence, there is no bare area to cause pain. In addition, the mild healing process results in minimal regression and avoids scarring problems.
The ablation profiles for the prior art PRK and LASIK laser treatments described above are based on mathematical equations and formulas that assume the eye as a perfect optical body or one that conforms to an optical model having very regular spherical shapes. The prior art ablation profiles thus fail to take into consideration the fact that each eye is unique and possesses many individual and general small and large irregularities. Because the prior art ablation profiles are based on fixed and regular ablation patterns, there can be created situations where excessive tissue is removed or insufficient tissue is removed. For example, in certain astigmatism situations there is a much larger defect on one side as compared to the opposite diametrical side. Thus, upon application of a normal, prior art laser ablation pattern for such a situation (an eliptical ablation profile), the ablation pattern would remove both the tissue causing the defect and tissue not associated with the defect, thus creating the possibility of a new defect in the eye following treatment.
Also, the corneal surface is not a very smooth body and has topographical irregularities which can be both large and small. Under the prior art laser systems these surface irregularities are not taken into consideration in the formulas and patterns designed to correct defects such as hyperopia, myopia and astigmatism. Accordingly, the final ablation profile formed in the eye will deviate to some extent from what was predetermined by the surgeon to be the final resultant profile of the eye, and this is particularly true with respect to eyes with highly irregular surfaces wherein the defect can be simply shifted to a lower corneal altitude and thus create a new defect which is often unpredictable under the prior art systems. This would be true for both PRK and LASIK treatments as in the former the laser would ablate deeper into the eye then what was originally contemplated in any valley area in the topography of the eye and not as deep as expected in any peak or protrusion area of the topography. With LASIK, the microkeratome is designed to remove a constant thickness flap by way of pressing down during the cutting or planarization process such that the topography of the external surface of the cornea is duplicated in the exposed corneal stroma therebelow.
Because the prior art systems rely on rigid patterns and formulas that are based on standard optical models, they limit the surgeon from fully exercising his clinical expertise during the determination of an ablation profile to be performed. In other words, they do not allow a surgeon to customize an ablation profile to best suit the surgeon""s clinical evaluation of the patients corrective requirements.
The prior art systems are also not well suited for many eye corrections that require fine detail or customized ablations particularly eye correction cases such as trauma, some congenital defects, and defects that arise due to accidents during eye surgery.
The following articles, patents and patent application provide additional background information and are incorporated herein by reference:
U.S. Pat. No. 4,721,370 (L""Esperance); U.S. Pat. No. 4,995,716 (Warnicki et al.); U.S. Pat. No. 5,133,726 (Ruiz et al.); U.S. Pat. No. 5,159,361 (Cambier et al.); U.S. Pat. No. 5,318,046 (Rozakis); U.S. Pat. No. 5,533,997 (Ruiz et al.) and U.S. Pat. No. 5,843,010 (Cambier et al.) and pending U.S. patent application No. 09/186,884 (now U.S. Pat. No. 6,302,877) to Luis A. Ruiz.
xe2x80x9cCorneal Topographyxe2x80x94The state of the Artxe2x80x9d James P. Gill et.al. Published by Slack Incorporated.
Chapter 3. xe2x80x9cCharacterizing Astigmatism: Keratometric Measurements Do Not Always Accurately Reflect Corneal Topography.xe2x80x9d 25-33.
Chapter 5. Thornton, Spencer P. and Joseph Wakil. xe2x80x9cThe EyeSys 2000 Corneal Analysis System.xe2x80x9d 55-75.
Chapter 7. Snook, Richard K. xe2x80x9cPachymetry and True Topography Using the ORBSCAN System.xe2x80x9d 89-103.
Chapter 9. Smolek, Michael K. and Stephen D. Klyce. xe2x80x9cThe Tomey Technology/Computed Anatomy TMS-1 Videokeratoscope.xe2x80x9d 123-48.
Chapter 16. Durrie, Daniel S., Donald R. Sanders, D. James Schumer, Manus C. Kraff, Robert T. Spector, and David Gubman. xe2x80x9cEvaluating Excimer Laser Procedures.xe2x80x9d 241-61.
Ren, Qiushi, Richard H. Keates, Richard A. Hill, and Michael W. Berns. xe2x80x9cLaser Refractive Surgery: A Review and Current Status.xe2x80x9d Optical Engineering, 34, 642-59 (1995).
Lin, J. T. xe2x80x9cCritical Review on Refractive Surgical Lasers.xe2x80x9d Optical Engineering, 34, 668-75 (1995).
Munnerlyn, Charles R., Stephen J. Koons and John Marshall. xe2x80x9cPhotorefractive Keratectomy: A Technique for Laser Refractive Surgery.xe2x80x9d J. Cataract Refract. Surg. 14, 46-52 (Jan. 1988).
Manns, Fabrice, Jui-Hui Shen, Per Soderberg, Takaaki Matsui, and Jean-Marie Parel. xe2x80x9cDevelopment of an Algorithm for Corneal Reshaping With a Scanning Laser Beam.xe2x80x9d Applied Optics, 34, 4600-08 (July 1995).
The present invention is directed at a system and method for corrective eye surgery that allows a surgeon to use his surgical expertise and familiarity with a patient""s individual requirements to design an ablation profile that is well suited for the situation. The present invention thus provides the surgeon with an extremely versatile tool which opens up to the surgeon a wide variety of surgical procedure options and thus enables the surgeon to customize each surgery to achieve what is considered under the circumstances to be the best clinical surgical procedure for that patient. In providing a highly customizable system, the present invention avoids restricting the surgeon to rigid ablation profiles which in some instances only lead to additional defects or fail to substantially improve the vision of the patient. Under the present invention the surgeon is able to direct the laser beam to produce the specific laser pattern deemed best suited for removing the tissue of the eye to achieve the best clinical result contemplated by the surgeon.
In addition, the present invention provides a highly accurate system that takes into consideration the topographical comeal surface irregularities that vary from patient to patient when performing any one of a wide variety of corneal curvature corrections. By taking the individual""s specific corneal topography into consideration there is better avoided the possibility at the post operative state of having remaining corneal topographical irregularities adversely altering the desired results of the surgery. Also, because the surgeon is able to negate the topographical irregularities from patient to patient a more precise and regularized result ensues from patient to patient.
The present invention also features a method and apparatus for calibrating or visualizing the performance of a laser beam in carrying out a laser beam ablation profile which includes the use of a substrate which presents different visual color cues as to what levels the laser beam will reach in carrying out the laser beam profile fed to the laser control system.
The present invention comprises a topographical device that is able to provide data characteristics of a corneal surface topography. Preferably the topographical device is an elevational topographic device that provides data characteristics as to the topography map of a patient""s external corneal contour in the form of an elevation map which is represented by a sufficient amount of elevational points with respect to an X-Y plane to provide an accurate representation of the actual topography of the eye. The data characteristics for the elevational map are then exported to the interface system of the present invention.
The interface system includes a topographer/interface input system that receives the exported data from the topography device. The topographer/interface input system extracts the data (e.g., x,v,z data) from the exported data received from the topographer, and preferably stores that data in the form of a matrix which is easy to process by the data processing system of the interface system.
The data processing system determines a fit reference sphere which can be an averaged or median sphere with respect to the peaks and valleys of the actual topography (e.g, a sphere that has an equal volume of tissue or peaks above the sphere as to the volume of the non-tissue or valley locations therebelow). A variety of techniques can be utilized to form the fit reference sphere such as a recursive spline-subdivision or a Bezier curve technique.
The interface system includes a visualization system linked to the data processing system so that, based on data fed from the data processing system, the visualization system provides a plurality of visual and interactive screens which enables a surgeon to manipulate and customize ablation profiles to achieve a particular profile that is considered by the surgeon to be the best ablation profile for that particular patient. With the data processing/visualization systems combination of the present invention the surgeon is able to view a variety of different ablation profiles which are considered possible solutions and is able to view simulated post operative views of each proposed ablation profile.
The data processing system includes a reference section or module that processes data concerning the interrelationship between the topographical contour determined by the topographer device and received by the interface system and a reference means such as the previously determined fit reference sphere. With the stored elevation data (e.g. a data matrix for both the actual contour and the fit reference sphere) two and/or three dimensional visual depictions are provided along any one of a plurality of possible eye axes for both the actual topography configuration and the fit reference sphere. The fit reference sphere is presented in a two dimensional view window of the visualization system as a straight line that is initially below (when a median fit reference sphere is chosen as the initial reference) the uppermost elevations of the topography profile shown in two dimensional form. This two dimensional representation of the fit reference sphere can be used as a starting or reference point for the surgeon to begin manipulating and viewing different ablation profiles required to remove the tissue from the topography contour down to the fit reference sphere. The interface system provides means for varying the relative position of the fit reference sphere with respect to the actual topographical contour. The variation between the two is preferably represented by a shifting of the height of the straight line representing the fit reference sphere within a two dimensional grid while the two dimensional profile configuration of the actual topography contour (taken along that same axis) stays fixed on that grid. At the same time, a plurality of screens show how the ablation profile and a simulated post operative eye contour would look upon each shift in position of the reference line (e.g., shifts along a one diopter elevational scale). The ablation profile and resultant eye contour configuration is preferably shown both in a two dimensional grid and a three dimensional depiction with the three dimensional depiction preferably being a topographical color depiction as to the diopter deviation for the eye contour and ablation profile across the cornea surface of the eye. The surgeon can thus determine the simulated effect on the overall resultant eye profile and the configuration and depth of the ablation profile required to achieve that final contour when a certain reference plane is utilized.
For example, the surgeon may shift the fit reference sphere down with respect to the actual eye topography representation which would appear in the two dimensional view screen as a lowering of the reference line with respect to the eye""s two dimensional topography profile taken along a common, predetermined eye axes. If, for example, the surgeon was to shift the reference line down to a height which corresponded to the deepest most point of the topography profile, the surgeon would be able to determine the maximum ablation depth required to carry out a correction that removed all topographical deviations at least along the axis being viewed. In certain situations, however, such as where there is a localized, very deep valley in the topography of the eye, there would be required too deep and/or large a volume of ablation such as where there is not much corneal stroma depth to work with (a post operative correction of an accident occurring in an earlier surgery). Accordingly the setting of the reference line to conform to the lowest topographical point in the surface of the eye may not be well suited for that patient despite that ablation profile being the best suited for removing all irregularities in the eye""s topographical contour.
It is here that the examiner can use his surgical expertise and familiarity with the patient to shift up the reference line to a location that presents the best clinical ablation profile under the circumstances. For example, the surgeon may shift the reference line a few diopters up (e.g., 5 diopters up) so as to remove a large percentage of any eye irregularities up above the reference sphere while avoiding any perceived problems with over ablation. The present invention makes it easy for the operator to determine when a potential problem may exist. For instance, a particular color can be assigned to any ablation depth that would involve having to go beyond a lower range point (e.g. 0.170 mm depth) whereby the view screen would provide a ready recognizable warning as to a potential problem. A separate screen pop up box with a question as to whether such a profile is desirable can also be provided. Situations might also arise where it is deemed better not to use the deepest valley point as the basis for picking the elevation of the proposed best clinical sphere on the basis that it would be more clinically desirable to take less volume off by shifting the proposed best clinical sphere up in elevation and relying on a more localized custom formula technique directed at negating any remaining aberration(s) remaining below the chosen best clinical reference sphere.
Together with the two dimensional view screen showing the reference line and topography profile interrelationship, there is preferably provided a sliding elevation deviation button and scale representation which can be computer mouse controlled to easily vary the height of the reference line with respect to the topography profile. A similar sliding scale arranged horizontally to allow an operator to vary the diameter of the proposed best clinical sphere is also preferably provided as well as number indicators as to the radius, curvature and relative position of the best clinical sphere with the fit reference sphere. The surgeon is thus able to easily also change the shape of the proposed best clinical sphere to induce either a flatter curve configuration or a steeper best clinical sphere configuration depending upon the surgeon""s clinical evaluation as to what type of curvature is best for correcting the eye without introducing any significant undesirable post operative effects and preferably removing the least amount of tissue required under the circumstances. The number view windows showing the radius value for the fit reference sphere, the diopter value for the fit reference sphere and the depth or elevation between the original position of the fit reference sphere to the presently displayed height position (a lower or superior position) are interrelated so that upon making a change in one category that results in a change in another category, the change is automatically made by the data processing system and the appropriate value displayed in the display area. Since the elevation between the original fit reference sphere and the actual topographical profile is know for each X-Y reference point and since the change in elevation of the proposed best clinical sphere with respect to the fit reference sphere is known for each point as well, there can readily be determined with elevation deviation monitoring means the difference in elevation (and hence the required total ablation) between the topography profile and the proposed best clinical sphere which is often, but not always positioned below the original fit reference sphere. It is the patient""s unique topographical contour and general eye shape coupled together with the desired input expertise of the surgeon that determines what is the best clinical sphere for that patient.
The reference section also includes an eye axes option provider which allows an operator to pick and choose which eye axes (typically an option between the Nxe2x80x94T (0) axis, the superior/inferior axis (90xc2x0), the 45-225xc2x0 axis and the 135-315xc2x0 axis. This option is designed for use with the best clinical sphere determination means of the present invention as it allows an operator to visualize simulated post operative results for a proposed best clinical sphere ablation profile along a variety of different axes.
For example, the surgeon may be confronted with a patient having an astigmatic profile along the superior/inferior axis which is apparent from a display on a base screen of the color differentiated diopter profile of the pre-operative eye. Recognizing this as an axis best suited for an initial best clinical sphere determination the operator can choose the superior/inferior axis upon which to review different relationships between the two dimensional and three dimensional illustrations of the actual topography, initially determined fit reference sphere and proposed best clinical sphere location. This would provide a good indication of the type of ablation profile that would be required to remove the astigmatic irregularity. This eye may also however have a localized very deep depression that does not fall anywhere along the chosen reference axis. If the proposed best clinical sphere profile presented along the inferior/superior axis is opted for, then this localized depression would be overlooked and remain such that there would remain some visual degradation due to the configuration of the corneal surface. If a check were made along an additional axis such as the 45 degree axis and the very deep localized valley fell along that axis, then the surgeon could make a clinical determination as to whether the best clinical sphere ablation profile should fall at the lowest depth point of the localized valley or whether that would create ablation depth profiles so as to warrant an intermediate best clinical sphere height somewhere above the lowest depth point and below the elevation determined for the superior/inferior axis. Accordingly, the surgeon is able to interact with the present invention to determine the best clinical sphere suited for the particular patient involved through, for example, determining which axis or axes to choose for viewing simulated results based on experience and the initial topography presented as well as determining whether or not a best clinical sphere should be placed at the lowest point on the topography profile or some alternate compromise setting which is deemed clinically more appropriate under the circumstances.
Furthermore, the best clinical sphere ablation profile can either be used alone if the surgeon deems that it is sufficient based on the patient""s situation or coupled with additional ablation characteristics. As an example, if a patient has an astigmatic creating configuration which is to be removed with a best clinical sphere setting, but that ablation profile would create at the same time a hyperopic over correction in the eye that situation can be offset by adding additional ablation profile directions to achieve a more myopic resultant eye based on an ablation profile that can be either one that is a standard clinical or xe2x80x9cnormalxe2x80x9d profile or one that is self generated by the surgeon in a customizing step such as by choosing various factors to alter an ablation profile or by choosing a saved profile (including an earlier surgeon self generated file of useable profiles or profiles provided initially with the interface system).